"When is his birthday?"

Translation: 他的生日是什么时候？

[RuhRoh1]

I've noticed "是" isn't used in all the same contexts as English. Can someone be more specific when using "是"?

[dordoom]

The main function of the verb 是 is to serve as a copula of two nominals, i.e. tell us that "sth is sth". It cannot be used with adjectives as a copula, as adjectives in Chinese work like verbs, e.g. 大 "big" is literally "to be big" with that English "to be" already being expressed within it.

[Rk5I3]

I'm kind of a beginner myself, but at least with adjectives you usually don't use it in positive sentences at all. With 不, you do use it with long adjectives but not with short ones. 我的字不好. vs. 他的西瓜不是新鮮.
If you do use it, it emphasizes what you're saying, like "(but) you ARE beautiful!"

[andrewwilson4529]

This helped me https://www.fluentu.com/blog/chinese/2015/07/09/shi-chinese/

[AndriLindbergs]

Is nobody monitoring these questions? 3 weeks and no reply! I have the same question.

[Jim952908]

什么 should be adequate for a date. No one asks the time for a birthday.

[jdebruycker]

什么 alone means "what" so without 时候 it isn't enough to mean "when". Probably a better way to ask this would be 几月几号

[nicholas_durette]

is the 的 necessary here?

[dordoom]

Yes. The 的 of possession can basically only be dropped when talking about family members; else should be used. It is better to always use it to not mistake.

[MelissaRosen]

Is 时候 necessary?

[Garagan]

If I understand it correctly, it is part of the "shen ma".
Shen ma alone is "what".
But here you need "when".
So you need the extra words to make it a "when".

[Zaldrizes2]

Just want to point out... again... users who are typing without using the word bank can't hear the difference between 他／她／它

[NathanRasm]

Is 什么时候 better than 几号? Why?